Pressure supply system for spray guns



Nov. 7, 1961 F. c. WOELFER 3,0 7

PRESSURE SUPPLY SYSTEM FOR SPRAY suns Filed Aug. 14, 1959 2 Sheets-Sheet1 INVENT OR.

nTmeA/Eys.

Nov. 7, 1961 F. c. WOELFER 3,007,647

PRESSURE SUPPLY SYSTEM FOR SPRAY GUNS Filed Aug. 14, 1959 2 Sheets-Sheet2 I /A P 12 4 34 W 34 17% 5 INVENTOR.

Wfi. Meg

ATTORNEYS.

3,007,647 PRESSURE SUPPLY SYSTEM FOR SPRAY GUNS Frank C. Woelfer,Cincinnati, Ohio, assignor to Balcrank, Inc., Marhurg, Cincinnati, OhioFiled Aug. 14, 1959, Ser. No. 840,487 Claims. (Cl. 239-329) Thisinvention relates to a distribution system for spray guns, wherein paintor other viscous liquids are pumped from a reservoir and advanced to oneor more spray guns to be projected in spray form upon the surface to betreated.

Systems of this type are in extensive use in industrial plants inapplying paint, lacquer, and other surface finishing compounds to themanufactured parts. In most instances, the spray guns are operated in aspecial enclosure having air exhaust means to prevent the paint fumesfrom spreading throughout the plant. The supply reservoir is usuallylocated at some point remote from the spray booth and the paint isadvanced under pressure to the spray guns by way of a conduit which maybe from 25 to 100 feet or more in length.

According to the conventional supply systems to which the presentimprovements are particularly directed, the reservoir is provided withan air-operated pump for forcing the paint under pressure from thereservoir, through the supply line to the spray gun. The spray gunincludes a trigger-operated valve for regulating the flow of paint andalso includes an air supply line which creates an air blast forprojecting the paint in spray form from the discharge nozzle of the gun.For simplicity of control,

the air-operated pump of the reservoir is of the stall type, that is,the pump is stopped under back pressure in the supply line when thevalve of the spray gun is closed. Because of viscosity and flowresistance, it is necessary to supply the paint under fairly highpressure to the supply line; hence, when the spray gun valve is closedto stall the pump motor, the back pressure which builds up in the supplyline causes the line or conduit to expand slightly. When the spray gunvalve is re-opened, the back pressure creates a momentary gush or surgeof paint through the spray gun, due to rapid contraction of the expandedsupply line. This surge has too much volume and velocity to be atomizedby the air blast; as a consequence, it issues as a solid high velocitystream from the nozzle and spoils the surface finish of the work and isalso wasteful of paint.

One of the primary objectives of the present invention has been toprovide a surge eliminator of simple construction adapted to beinstalled in the distribution system to eliminate the surge problemwithout requiring extensive changes in the system or in the pump itself.

According to the present invention, the surge eliminator is inserted inthe supply line at some point between the pump and spray gun. The surgeeliminator blocks the flow of paint from the pump in response topredetermined back pressure in the supply line which is substantiallyless than the output pressure of the pump and insufficient to causeexpansion of the supply conduit. Accordingly, when the valve of thespray gun is closed, the surge eliminator immediately responds to theback pressure to stall the pump, and when the valve is reopened, thepaint immediately is supplied to the gun but at sufficiently lowpressure to eliminate the gush of paint. When the line pressure dropssufficiently, the valve of the surge eliminator opens to allow the pumpto resume operation.

The present surge eliminator is somewhat similar to the pressure controlunit shown in Patent No. 2,726,790, issued on December 13, 1955 to FrankC. Woelfer, the present applicant. According to the patent, the pressurecontrol unit is mounted upon a grease gun and includes dfihlhd? PatentedNov. 7, 196i.

a manually shiftable sleeve which, in one position, provides highpressure grease delivery and in a second position, provides a lowpressure delivery. The present surge eliminator differs from the controlunit in that it provides automatic operation, as distinguished frommanual, and also differs structurally to adapt it to its particular use.

Briefly, the surge eliminator of this invention comprises an externalshell or housing adapted to be inserted in the supply line, and aone-piece combined floating plunger and valve slidably confined withinthe shell, the plunger having two diameters which act as differentialpistons. The shell is bored internally to provide two cylinder bores forthe respective pistons and the intake end of the shell forms a valveseat which coacts with the end of the small diameter piston to controlthe operation of the pump. When the spray gun valve is opened, theplunger is shifted to an intermediate balanced position to allow thepaint to flow, and when the flow of paint through the line is blockedoff at the spray gun, the end of the small piston immediately engagesits valve seat to stall the pump.

A further objective has been to provide a simplified structure and onewhich reduces turbulence and flow resistance through the surgeeliminator.

For this purpose, the small diameter piston has a tapered nose whichcoacts with the valve seat and includes a series of radially spacedapertures formed in the nose rearwardly of the seat-engaging portion ofit. The apertures communicate with an axial bore formed in the plunger,the arrangement being such that the paint flowing through the valve seatenters the small cylinder and flows without much change in direction,about the tapered nose and through the radial apertures and through thecentral aperture to the discharge end of the shell.

By virtue of its structural features, the surge eliminator is alsoadapted to be installed in supply systems for highly viscous compounds,such as undercoating and sealing compounds of various kinds, which byreason of flow resistance, must be pumped through the lines at higherpressures than paint and the like. In such installations, the surgeeliminator may be installed between the outer end of the supply line andthe spray gun so as to maintain the supply line at full pump pressurefor immediate flow when the spray gun valve is opened. According to thisarrangement, the viscous material may cause expansion of the supply lineat full pump pressure; however, the surge eliminator prevents surging ofthe material through the spray gun when the valve is opened. The variousfeatures and advantages of the present invention will be more clearlyapparent to those skilled in the art from the following detaileddescription taken in conjunction with the drawings.

In the drawings:

FIGURE 1 is a diagrammatic view showing a typical paint delivery systemincluding a paint pump and spray gun, the surge eliminator beinginserted in the supply line adjacent the paint pump.

FIGURE 2 is a side view of a spray gun similar to FIGURE 1, but showingthe surge eliminator inserted in a second position, between the end ofthe conduit and spray gun.

FIGURE 3 is an enlarged longitudinal sectional view of the surgeeliminator, with the plunger in its unseated position during operationof the spray gun.

FIGURE 4 is a sectional view similar to FIGURE 3,

I but showing the plunger shifted to valve closing position in responseto back pressure when the spray gun is shut off.

FIGURE 5 is a cross sectional view taken along line 55 of FIGURE 4,detailing the tapered nose of the plunger.

Described generally with reference to FIGURE 1, the paint reservoir,indicated generally at 1, includes an air-operated pump motor 2 mountedat its upper end, the motor having a pump cylinder 3 projectingdownwardly toward the bottom of the reservoir. A paint pump of this typeincludes a piston slidably mounted within the cylinder 3 and connectedmeans of a piston rod to an air-actuated piston within the motor 2. Airpressure is supplied to the cylinder of the pump motor by an air conduit4 and is conducted by way of a suitable reversing valve arrangement tothe motor cylinder to reciprocate the pump piston.

The internal construction of the air motor and pump does not form a partof the present invention and has therefore been omitted from thedisclosure. It will be understood at this point however, that the motoris of the stall type arranged to advance the paint or other materialunder pressure to the supply conduit 5 which leads to the spray gun 6.When the spray gun valve is closed, it blocks the flow of paint throughconduit 5 and stalls the air motor under back pressure. In the exampleshown in FIGURE 1, the surge eliminator, which is indicated generally at7, is inserted between the delivery fitting 8 of the paint pump and theconduit 5.

The spray gun 6 is a conventional structure especially designed tohandle paints and other more viscous compounds, such as undercoatingcompounds for automobile bodies, roofing compounds, sealing compoundsand materials of the type used in Waterproofing the foundation ofbuildings. The word paint, as used in the specification and claims, isintended to also include these liquids and semi-liquids. These materialsare forced from the reservoir to the spray gun at pressures which dependupon the viscosity of the material and the length of the conduit. Thedelivery pressure is adjusted by suitable regulating means on thedelivery pump.

By way of example, in handling highly viscous materials such as anundercoating compound, Where the delivery conduit is fairly long, a pumpdelivery pressure in the neighborhood of 400 p.s.i. may be required toadvance the material through the conduit, due to the flow resistance ofthe material. On the other hand, in handling lighter liquids such asordinary paints and lacquer, considerably less delivery pressure isrequired. In either case, in the absence of a surge eliminator, theconduit 5 expands slightly under back pressure when the spray gun isshut off, with the pump stalled under back pressure. When the spray gunvalve is re-opened, the conduit contracts rapidly and as a consequence,projects a gush or surge stream of paint through the nozzle 10 asconduit pressure drops to normal. The surge eliminator of this inventionprevents this surge by reducing the back pressure in the conduit 5sufliciently to prevent expansion of the conduit under back pressure.

In general, the spray gun comprises a body having a spray nozzle 10, acontrol handle 11, and an air conduit 12 which supplies air pressure forprojecting the paint in the 'form of a spray for application to thesurface to be coated. The spray gun is provided with suitable valves(not shown) interconnected with the control handle 11 to regulate theflow of air and paint through the gun, both valves normally being closedand being opened only when the operator actuates the handle 11. When thevalves are opened, the paint enters the gun and is picked up in a blastof air and projected as a fine mist from the nozzle 10. When the valvesare closed, the flow of air and paint are blocked off, as noted above,thus creating back pressure in conduit 5 so as to stall the pump.

When the surge eliminator 7 is installed at the point shown in FIGURE 1,the eliminator responds to a given back pressure in the conduit 5 tostall the pump which delivers at a higher pressure. The surge eliminatortherefore decreases the back pressure in the conduit to a point belowthat at which conduit expansion occurs. As a consequence, the paint inthe conduit is maintained at all times under a predetermined normaldelivery pressure to provide immediate response when the spray gun valveis opened, but sufliciently low to eliminate the surge when the spraygun is started.

Surge eliminator Referring now to FIGURES 3-5, the surge eliminator ingeneral comprises a cylindrical housing or shell 13, having adifferential plunger, indicated generally at 14, and a closure cap 15screw threaded as at 16 upon the outlet end of the shell 13. The inletend of the shell comprises an externally threaded nipple 17 which isscrewed into the delivery fitting 8 of the pump, as indicated earlier.The intake nipple 17 leads to a valve seat 18 which communicates with asmall cylinder bore 20. The opposite end of the small cylinder 20 isdelineated by a tapered shoulder 21 which leads to a large cylinder bore22. The closure cap 15 includes an internal shoulder 23 which delineatesthe outer end of the large cylinder 22. Shoulder 23 leads to a deliveryfitting 24 which is internally threaded as at 25. The conduit 5 isprovided with a fitting which includes a nipple 26 threaded into thefittings 24. In order to provide wrench engagement for tightening theclosure cap 15 upon the shell 13, both parts are provided with flats 27(FIGURE 5) which are machined across the cylindrical outside diameter ofthese parts.

The floating valve plunger, indicated previously at 14, is free to floataxially within the shell 13, being slipped in place before the closurecap 15 is applied. The plunger comprises a small piston 30 interfittingthe small cylinder bore 20, and a large piston 31 interfitting the largecylinder bore 22. The small diameter piston 30 has a tapered nose 32projecting toward the intake nipple I7 and adapted to interfit the valveseat 18, thereby to block the flow of paint, as indicated in FIGURE 4.

The plunger includes an internal bore 33, and the tapered nose isprovided with apertures 34 communicating with bore 33. It is to be notedthat the apertures 34 are located inwardly of that portion of thenosepiece which engages the valve seat 18. As viewed in FIGURE 5, theapertures 34 are equally spaced about the periphery of the nose 32 andhave axes residing at right angles to the tapered surface of the nose,such that the apertures partially face the valve seat 18. When the valveis open (FIGURE 3) the paint flowing through the valve seat is deflectedoutwardly by the tapered nose and enters the small diameter cylinder 20then is deflected by the cylinder wall inwardly through the apertures 34and into the bore 33 of the plunger. The arrangement is such that thepaint flows with little interference or turbulence through the valveseat and plunger to the outlet end of the unit, as indicated by thearrows.

The pistons 30 and 31 each include a peripheral groove 35 having seatedtherein an O-ring 36 formed of synthetic rubber or other appropriatematerial. These rings provide a seal with the surface of the respectivecylinder bores, while permitting the plunger to slide freely therein. Anannular space 37 is delineated within the shell 13 by the juncture ofthe two pistons and their cylinder bores. A small aperture 38communicates with the annular space to permit the escape of any paintwhich may leak past the seal n'ngs during operation of the valves, andto prevent aid from being trapped therein.

In its full open position shown in FIGURE 3, the rearward end of theplunger seats against the internal shoulder 23 of the closure cap 15.This portion of the plunger is counterturned externally as at 40 and isprovided with a lateral aperture 41 to provide communication between thecylinder and annular space delineated by the counterturned portion ofthe piston.

Although the plunger is shown in FIGURE 3 at its limit of motion towardthe left, in actual practice, it will shift to an intermediate position,as explained below.- The differential piston diameters, in the exampleillustrated, provide a pressure ratio of 2 to 1 in pump deliverypressure to conduit pressure. By way of example, if the pump is set todeliver paint at 400 p.s.i., the valve will remain open until a backpressure of approximately 200 p.s.i. exists in conduit 5. At thispressure, the differential areas of the two pistons are effective toshift the plunger toward the right, causing the nose to establish a sealwith the valve seat 13 thereby to stall the pump. During operation ofthe spray gun, there is always a tendency for the plunger to shifttoward closing position under the back pressure acting upon the largepiston 31. On the other hand, the pump pressure acts upon the smallpiston 3t) in the opposite direction to keep the valve partially openand in a state of equilibrium, with greater pressure acting upon thesmall piston in the ratio of the diiference in piston diameter. However,when the plunger shifts to closed position, the forces acting upon theplunger consist of the pump pressure multiplied by the area of the nosewhich engages the valve seat, opposed to the back pressure acting uponfull diameter of the large piston.

When the spray gun valve is opened, the back pressure in the conduitimmediately starts the flow of paint to the nozzle, and at the sametime, the back pressure on the large piston 31 decreases, permitting theplunger to shift again toward the left so as to reestablish the supplyto the conduit.

In handling heavy viscous compounds, such as semiliquid compounds whichhave a great deal of flow resistance, a higher pressure is required toforce the compound through the conduit, as noted earlier. In such cases,the surge eliminator is interposed between the end of the conduit andthe spray gun, as indicated in FIGURE 2. In this arrangement, the fullpump pressure is available to force the compound through the conduit 5,while on the other hand, the surge eliminator prevents any gush ofmaterial when the spray gun is started. During actual operation, theflow resistance of the material causes the pressure to dropsubstantially as the material advances toward the end of the conduit.Accordingly, if the surge eliminator were interposed at the pump end ofthe conduit, the flow resistance would retard the build-up of pressurein the conduit and thereby introduce a lag in the operation of the spraygun.

The surge eliminator is also introduced in the outer end of the supplyline in those instances where the line must be extended for asubstantial distance beyond the pump, as is the case in certainindustrial installations. In this instance, even tho-ugh paint ofaverage consistency is being pumped, the length of the supply conduitwill create sufiicient flow resistance to introduce a time lag in thepressure build-up. With the unit at the outer end of the line, the backpressure maintained in the line is available for immediate response tooperation of the spray gun.

Having described my invention, 1 claim:

1. A supply system for paint and the like comprising a paint reservoir,a supply conduit, a power pump associated with the reservoir and adaptedto deliver paint from the reservoir to the conduit under pressure, aspray gun in communication with said conduit for projecting the paint inthe form of a spray, said spray gun having a valve for blocking the flowof paint through the spray gun, said power pump adapted to stall underback pressure when said spray gun valve is closed, a surge eliminator incommunication with said conduit between the pump and spray gun, saidsurge eliminator comprising a housing having an inlet passageway at oneend thereof including a valve seat, said housing having an outletpassageway at the opposite end thereof, an axially floating one-piecepressure-responsive plunger residing within said housing, said plungerhaving a pair of axially aligned dilferential diameter pistons atopposite end portions thereof slidably confined in said housing insealed engagement therewith, the larger of said pistons being presentedto said outlet passageway, and a tapered nose element on the smallerpiston of said plunger adapted to engage said valve seat, said plungershifting said nose element am'ally into engagement with said valve seatin response to back pressure when the spray gun valve is closed, saidback pressure being substantially less than the delivery pressure of thepower pump, said nose element thereby stalling said pump under backpressure which is insufiicient to create a surge of paint through thegun when the valve thereof is opened.

2. A supply system for paint and the like comprising, a paint reservoir,a supply conduit, 9. power pump associated with the reservoir andadapted to deliver paint from the reservoir to the conduit underpressure, a spray gun in communication with said conduit for projectingthe paint in the form of a spray, said spray gun having a valve forblocking the flow of paint through the spray gun, said power pumpadapted to stall under back pressure when said spray gun valve isclosed, a surge eliminator interposed between the inlet end of saidconduit and the pump, said surge eliminator comprising a housing havinga pair of axially aligned differential diameter cylinder bores formedtherein, said housing having an inlet passageway at one end thereofincluding a valve seat communicating with the smaller of said cylinderbores, said housing having an outlet passageway at the opposite endthereof communicating with the larger of said cylinder bores, an axiallyfloating pressure-responsive plunger residing within said housing, saidplunger having differential diameter pistons slidably confined in saidcylinder bores, and a tapered nose element on the smaller of saidpistons, said tapered nose adapted to engage said valve seat, saidplunger having an axial bore extending to said tapered nose, said nosehaving a plurality of apertures communicating with the bore of theplunger, said apertures having axes inclined toward said valve seat,said plunger shifting said nose element axially into engagement withsaid valve seat in response to back pressure in the conduit when thespray gun valve is closed, said back pressure being substantially lessthan the delivery pressure of the power pump, said nose element therebystalling said pump under back pressure which is insufficient to create asurge of paint through the gun when the valve thereof is opened.

3. A supply system for paint and the like comprising a paint reservoir,a supply conduit, a power pump associated with the reservoir and adaptedto deliver paint from the reservoir to the conduit, a spray gunconnected to said conduit for projecting the paint in the form of aspray, said spray gun having a valve for blocking the flow of paintthrough the spray gun, said power pump adapted to stall under backpressure in said conduit when said valve is closed, a surge eliminatorinterposed between the outlet end of the conduit and spray gun, saidsurge eliminator comprising a housing having a pair of axially aligneddifferential diameter cylinder bores formed therein, said housing havingan inlet passageway at one end thereof including a valve seatcommunicating with the smaller of said cylinder bores, said housinghaving an outlet passageway at the opposite end thereof communicatingwith the larger of said cylinder bores an axially floating pressureresponsive plunger residing within said housing, said plunger havingdifferential diameter pistons slidably confined in said cylinder bores,and a tapered nose element on the smaller of said pistons, said taperednose adapted to engage said valve seat, said plunger shifting said noseelement axially into engagement with said valve seat in response to backpressure in the spray gun when the valve thereof is closed, said backpressure being substantially less than the delivery pressure of thepower pump while the pressure in said conduit is equal to the pumpdelivery pressure, said nose element thereby stalling said pump underback pressure which is insufiicient to create a surge of paint throughthe gun when the valve thereof is opened.

4. A surge eliminator for a supply system for paint and the likeincluding a supply conduit, a power pump adapted to deliver paint to theconduit under pressure, and a spray gun connected to said conduit andhaving a valve for blocking the flow of paint therethrough, said surgeeliminator comprising, a housing having a pair of differential diametercylinder bores in end-to-end relationship, said housing having an inletpassageway at one end communicating directly with the smaller of saidcylinder bores and an outlet passageway at its opposite endcommunicating with the larger of said cylinder bores, said housingadapted to be inserted in said conduit between the pump and spray gunfor the passage of paint through the housing from the inlet passagewayto said outlet passageway, said inlet passageway having a valve seatfacing the end of the smaller cylinder, a one-piece axially floatingpressure-responsive plunger having a pair of differential diameterpistons slidably confined in said differential cylinder bores, thelarger of said pistons being presented to the outlet passageway andadapted to be shifted therefrom in response to predetermined backpressure in said outlet passageway, and a tapered nose on the smaller ofsaid pistons adapted to engage said valve seat, said tapered noseincluding a series of apertures having axes inclined toward the inletpassagewa, said plunger having an axial bore communicating with saidapertures and providing for the flow of paint generally in a straightline from the inlet passage, about said tapered nose and through saidapertures when the nose is spaced from the valve seat with the spray gunvalve open, said plunger adapted to shift said nose into engagement withthe valve seat in response to back pressure in the conduit which is lessthan the delivery pressure of said pump, said back pressure beinginsufficient to create a surge of paint through the gun when said valveis re-opened.

5. A surge eliminator for a pressure supply system for paint and thelike including a supply conduit, a power pump adapted to deliver paintto the conduit under pressure, and a spray gun connected to said conduitand having a valve for blocking the flow of paint therethrough, saidsurge eliminator comprising, a housing having a pair of differentialdiameter cylinder bores in end-to-end relationship, said housing havingan inlet passageway at one end communicating directly with the smallerof said cylinder bores and an outlet passageway at its opposite endcommunicating with the larger of said cylinder bores, said housingadapted to be inserted in said conduit between the pump and spray gunfor the passage of paint through the housing from said inlet passagewayto said outlet passageway, said inlet passageway having a valve seatadjacent said smaller cylinder and facing the same, and an axiallyfloating pressure-responsive plunger having differential diameterpistons slidably confined in said cylinder bores, the larger of saidpistons being presented to the outlet passageway and adapted to beshifted therefrom in response to predetermined back pressure in saidoutlet passageway, the end portion of the smaller of said pistons beingtapered from the full diameter of the smaller cylinder bore toward thevalve seat, said tapered end portion adapted to engage said valve seat,said tapered portion having a plurality of apertures located inwardlyfrom the portion thereof which engages the valve seat, said plungerhaving an axial bore communicating with said apertures and extendingtoward said outlet passageway for the passage of paint generally in astraight line from the inlet passageway about the said tapered portionand through said apertures when the nose is spaced from the valve seatwith the valve of the spray gun open, said plunger adapted to shift saidtapered portion into engagement with the valve seat in response to backpressure which is less than the delivery pressure of said pump, saidback pressure being insufficient to create a surge of paint through thegun when said valve is re-opened.

References Cited in the file of this patent UNITED STATES PATENTS922,986 Westaway May 25, 1909 1,971,659 Ruthven Aug. 28, 1934 2,266,354Christenson Dec. 16, 1941 2,404,548 Thomas July 23, 1946 2,687,739Shelburne et al Aug. 31, 1954 2,793,075 Gulick May 21, 1957

